<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
<input id="aaa" type="text">
<button id="bbb" onclick="show()">666</button>
<script>
    function show() {
        document.getElementById('aaa').focus()
    }
</script>
</body>
</html>